1. Field of the Invention
The invention relates to a controllable coolant pump driven by way of a belt pulley.
2. Description of Related Art
In the state of the art, controllable coolant pumps for internal combustion engines are previously described, which are driven by the crankshaft of the internal combustion engine by way of a belt pulley, and in which the impeller wheel is driven by the pump shaft in switchable manner, for example in connection with a friction pairing.
The applicant presented a proven controllable coolant pump in the patent DE 100 57 098 C1, in which a magnetic coil is disposed in the pump housing, in stationary manner, which coil can enter into an action connection with an anchor disk that is disposed on the drive shaft so as to rotate with it, but is displaceable under spring force, provided with a friction coating on the impeller wheel side, in such a manner that when the magnetic field is shut off, the impeller wheel that is disposed on the drive shaft so as to rotate is entrained by the anchor disk as a result of the spring press-down pressure.
Since, in the case of this construction, the entrainment friction moment is greatly limited by the magnetic construction space that is available, this solution was developed further in systematic manner.
The application DE 102 35 721 A1 that builds on this solution describes a controllable coolant pump which has been optimized in terms of construction space, having a drive torque that can be transferred from the friction disk of the magnetic coupling to the impeller wheel, which torque is clearly increased.
This increased drive torque is brought about by means of increasing the press-down force, which results from the fact that a partial vacuum that supports the press-down force is built up between the friction disk and the impeller wheel, by means of an inflow ring and an outflow ring for the cooling medium, and, at the same time, the friction disk has the pressure of the cooling medium applied to it during operation, by means of overflow openings on the coupling side.
Both the cooling power and the drive power of the coolant pump can be varied by means of the two-point regulation that can be implemented with such coolant pumps.
However, optimal regulation of the drive power or cooling power of coolant pumps for motor vehicles is supposed to make it possible to avoid compulsory cooling that starts immediately when the engine is started, causing the warm-up phase of the engine, with all the disadvantages that occur during this phase, such as increased friction losses, increased emission values, and increased fuel consumption, to be clearly reduced.
In order to now allow such faster engine warm-up, with the advantages that result from it, the drive of the coolant pump was uncoupled during cold start of the engine, with the aforementioned constructions.
Once the engine reached its operating temperature, the friction coupling, with the wear problems inherent to this coupling construction, as a result of its function, was activated, and the drive of the coolant pump was turned on.
In this connection, a large amount of cold coolant was now pumped into the engine, which had heated up to operating temperature, so that the engine immediately cooled down greatly.
When this happened, however, the desired advantages of rapid warm-up of the engine were partially compensated again.
When larger coolant pumps were turned on again, great torques furthermore had to be overcome, because of the required mass acceleration, and this necessarily resulted in great component stress. A solution was previously described in U.S. Pat. No. 4,828,455, in which it was possible to change the active impeller width of the impeller wheel by means of a slit, axially movable disk.
A controllable coolant pump having an open impeller wheel and an adjustable slide having a slit, axially movable base, with which the effective impeller width of the impeller wheel can be varied by means of electrical, hydraulic, or pneumatically activated displacement of the slide is also known from DE 199 01 123 A1.
One of the significant disadvantages of the two aforementioned constructions is, however, that slit slides can only be used in connection with simply curved, open vane wheels.
However, such simply curved vane wheels necessarily have a low degree of effectiveness.
Another construction of a slide was presented by the applicant in DE 103 14 526 A1. This is a valve slide that is electromagnetically activated and works in the suction region of a coolant pump.
In the case of large pump units in systems technology and power technology, other constructions of valve slides are used (cf. “Die Kreiselpumpen” [Impeller-driven pumps] by C. Pfleiderer, Springer-Verlag, 4th edition (1955), p. 422).
These constructions, referred to as split slides, are axially displaceable valve slides disposed concentric to the impeller wheel, which are supposed to prevent exit of the fluid from the impeller wheel into the pressure spiral in the closed position, and are used to block off the volume stream.
In DE 881 306 C, for example, such an axially movable, spring-loaded, hydraulically adjustable split slide that works in the pressure region is previously described, which is able to greatly restrict the transport volume stream under a spring effect, while taking advantage of the differential pressure of the wheel side space.
However, these solutions of impeller-driven pump technology are not suitable for use as a coolant pump in motor vehicle technology, since, among other things, the slide closes as a result of the spring effect, for example, so that a failure of the control necessarily also means a failure of the coolant pump, and continued operation of the coolant pump after failure of the control (fail-safe) cannot be guaranteed.
Furthermore, in the case of this construction, the guides are always exposed to the operating medium, with the unavoidable contaminant load of the cooling medium, such as molding sand, metal particles, and the like, from the production process, for example, or resulting from wear, so that dirt particles that penetrate into the guides necessarily lead to jamming of the slide.
Furthermore, no “zero leakage” can be implemented with these slides previously described in the state of the art, in the closed state.
In the course of the increasing optimization of internal combustion engines with regard to emissions and fuel consumption, however, it is becoming increasingly important to bring the engine to operating temperature as quickly as possible after a cold start, in order to minimize friction losses, on the one hand (with an increasing oil temperature, the viscosity of the oil decreases, thereby decreasing the friction on all oil-lubricated components), and reducing the emission values (since the catalytic converters only go into effect after the so-called “starting temperature”, the time period until this temperature is reached significantly influences the exhaust gas emissions), in order to thereby simultaneously reduce the fuel consumption.
Test series in engine development have shown that a very effective measure for warming the engine is that of “standing water” or “zero leakage” during the cold-start phase.
In this connection, coolant should by no means flow through the cylinder head during the cold-start phase, in order to bring the exhaust gas temperature to the desired level as quickly as possible.
Leakage gas flows of less than 0.5 l/h (“zero leakage”) are desired by vehicle manufacturers.
Studies concerning the fuel consumption of internal combustion engines in motor vehicles have also shown that about 3 to 5% fuel can be saved by means of consistent thermal management, in other words those measures that result in optimal operation of an internal combustion engine in terms of energy and thermomechanics.
Therefore, ever more precise regulation of the coolant throughput as a function of the temperature of the coolant being passed through is absolutely necessary, taking these aspects into account.